Giant aneurysms (> 2.5 cm) represent only 5-7% of all aneurysms. Nevertheless, their management is rather difficult due to their atypical natural history and peculiar treatment. Clinical history of giant aneurysms does not differ from that of the smaller ones regarding the incidence of subarachnoid hemorrhage, but it is complicated by much more neurologic deficits and by the occurrence of chronic intracranial hypertension syndrome. Diagnosis is essentially based upon CT scan and MR imaging in order to detect the morphological mass features and anatomical relationships, and upon angiography to appreciate characteristics regarding arterial flow and vascular relationships. The goal of treatment lies in the exclusion of the aneurysmal sac from the blood-stream and in the reduction of the mass effect. The treatment may be either surgical, endovascular or both. The most common surgical techniques consist in the direct occlusion of the neck of the aneurysm by means of metallic clips, or by fastening or trapping the carrier vessel or by removing the aneurysmal sac with the reconstruction of the arterial aspect when severe mass effect is detectable. The use of endovascular techniques goes for occlusion of the carrier vessel with balloons or for dynamic study of the collateral vascular districts with temporary occlusions.